This invention relates to a cutting insert for a slot milling tool, whose basic form is a parallelpiped, comprising two opposed side surfaces and four end surfaces extending therebetween, a first cutting edge provided at or near the line of juncture between adjacent end surfaces, second cutting edges defined by the lines of juncture between the side surfaces and an end surface provided with a chip surface.
Conventional cutting inserts of the above identified type are afflicted with disadvantages. Conventional slot milling tools either have a wide cutter body to receive an insert, inserted with a large relief angle giving a wide slot and little flank wear or a narrow cutter body able to receive an insert, inserted with only a small relief angle giving a narrow slot and much flank wear. Milling of a narrow slot in a work piece demands a narrow cutter body and a small relief angle for the inserts held in the cutter body. The small relief angle will accelerate the flank wear on the surfaces surround the cutting edges during milling with conventional inserts. Besides an unavoidable wear of the main cutting edge, the side surfaces of the insert will also be worn as they increasingly rub against the walls of the slot, causing large axial cutting forces on the cutting insert and the cutter body due to increased friction. The friction develope heat on the insert and in the slot and this results in a premature insert breakdown due to fragmentation, plastic deformation, etc.